Reducing the crystallinity of native fibrous cellulosic material



Patented Jan. 1, 1952 REDUCING THE CRYSTALLINITY OF NATIVE FIBROUSCELLULOSIC MATERIAL Kyle Ward, Jr., and Carl M. Conrad, New Orleans, andLeon Segal, Metairie, La., assignors to the United States of America asrepresented by the Secretary of Agriculture No Drawing. ApplicationAugust 8, 1950,

Serial No. 178,339 r Claims. (Cl. 260--212) (Granted under the act ofMarch 3, 1883, as

, l 1 The invention herein described may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes throughout the world, without the payment to us of 'any royaltythereon.

- This invention relates to native fibrous cellulosi'c material, inparticular cotton, linen, ramie, and other vegetable fibrous materials,in which the crystal form of cellulose I (native cellulose), as well asthe fibrous structure, of the original native material is retained butin which the degree'of crystallinity is reduced.

The objects of the present invention are, first, to provide a fibrouscellulosic material, such as cotton, in-which the original high degreeof crystallinityof 85-80% has been reduced to varying and controllabledegrees down to as low as" about and where such reduction has beenretained to a greater or less degree after completionof the treatmentsnecessary to accomplish the reduction; second, to prepare thiscellulosic material of low crystallinity in a manner such that there issubstantially no chemical degradation and substantially no loss orimpairment of the fibrous structure; and third, to prepare thiscellulosic material of low crystallinity without changing the crystalform from that of celluloseI (native 'cellulose) ,For an understandingof the present invention, an exposition .of the present view ofcellulose, as it occurs in nature, especially in the vegetable fibers,is pertinent; Such cellulose is considered to be composed of twomodifications, or phases. One of these is the dense crystalline ,phase,giving rise to characteristic X-ray diffraction patterns, and believedto consist of minute fibrous crystals, composed of many parallelcellulpse molecules,Qlying side by side, and held together in exactrelation by forces known as hydrogen bonds. The crystals are not, infact. discrete, but are considered to be connected by long cellulosemolecules which, in proceeding from one end of the moleculeto theother,fmay pass through a dozen or more crystallites andintercrystalline regions. There is produced,"thus, a discontinuouscrystalline structure, held together by the interconnecting, but widelydiverging, cellulose chains. The intercrystalllne portions of thecellulose molecules constitute a continuous network, and thus representthe less dense. so-called, amorphous modification or *phase. .Unllkethe"crystalline fraction, thls lat- LtrFphasegjives rise to a broad halowhenirradiated in the X- raybeam,

' One of the principaldrawbac'ks of the native amended April 30, 1928;370 O. G. 757) cellulosic fibers is their brittleness and tendency tofail when subjected to combined strain and shock. Thus, in spite of thegreat strength of such cellulosic fibers as fiax and ramie, they havenever attained much use in automobile tires and'other mechanical fabricsdue to their inability to resist shock. This shortcoming is consideredto be associated with the high degree of crystallinity of these fibers,being in the range of 90-95%. Cotton fibers do not show the degree offailure from shock that is shown by the flax, ramie, and other bestfibers generally, and

this is believed to be due to the somewhat lower crystallinity of cottonfibers, which vary from -90%. However, it is considered that thecrystallinity of cotton fiber, notwithstanding its somewhat lower value,is nevertheless considerably greater than optimum, and that a materialimprovement would be accomplished by the production of a fiber otherwisethe same, but lower in crystallinity.

The crystallinity of cotton fiber, and native cellulosic fibersgenerally, militates against their maximum usefulness in still anotherway. The fibers are dense and rather impervious to gases, liquids,reagents, etc. This is manifest in a number of ways. Cotton fibers,together with cellulosic fibers in general, as is well known, are ratherpoorly sensitive to dyeing, and. must be dyed with certain substantivedyes, i.. e., dyes that will adsorb on cellulose, or with mordant dyes.It is believed that the relatively large dye molecules cannot penetratethe crystalline areas, but only the relatively large areas, crevices,and pores existing in the amorphous areas. Many types of dye moleculesbeing relatively small can pass into the amorphous areas, but due to theopen structure, can pass out readily and are not retained on removal ofthe dye bath and washing. Since the amorphous areas can thus beconsidered to be the active adsorbing center of the acted in the fibrouscondition with such reagents as acetyl, propionyl, butyryl and benzoylanhydrides; methyl, ethyl, and proplonyl alcohols; and numerous othersubstances. Forexample,

lthe acetylation reaction, as is well-known, takes place very rapidly upto an extent corresponding approximately to the amount of amorphouscellulose present, and then much more slowly throughout the remainder ofthe reaction. The interpretation is that the reaction occurs principallyin the amorphous areas and perhaps on the surfaces of the crystallites.If the cellulose were first transformed into a product with a highproportion of amorphous cellulose, it is considered that the rate ofreaction could be greatly acc'er erated and the cost of manufacturecorrespondingly reduced.

It is considered, in fact, that all reactions withfibrous cellulose musttake place in two ways; first, very rapidly in the accessible, exposed,regions, i. e., in the amorphous areas; and secondly on the surfaces ofthe crystallites, by a much slower topochemical reaction. The surfacesof the crystallites being necessarily small in comparison with thesurfaces exposed by the amor phous regions, it follows that the relativeproportion of the latter must be the predominant factor in determiningease and rate of reaction. Any process which generates amorphouscellulose at the expense of the erystalline fraction must facilitate andfavor the desired reaction.

In genera according to the present invention, the native fibrousc'ellulosic material, particularly cotton, is treated by immersion in ananhydrous, liquid primary alkylamine containing 1 or 2 carbon atomspreferably primary ethylamine, er in a mixture. of such amines and ananhydrous primary alkyl amineeontaining 6 or '7 carbon atoms, preferablyprimary hexylamine. A substantial amount of the treating agent is thenmechanicallyremoved from the treated material, substantially all of theremaining agent being removed by extraction with a non-polar solvent,such as chloroform, This produces a fibrous ,cellulosic material withcrystallinity ranging from about 20% to about 59%, according to theconditions of treatment. Reduction of crystallinity varies with-the timeof immersion in the amine, periods of from 4 16 hours resulting in thelowest crystallinity. The physicalcondition of the fiber duringtre'atmentis such that handling is not dimcult. There are no visiblesigns of fiber damage, which fact is verified by the results of acceptedtests on the material.

X-ray diffraction patterns of such treated celluloses are those ofcellulose I, but; the heights ,of the characteristic. difiraction peaksare much reduced, indicating reduced crystallinitiesinqualitativeagreement with the results of the principal crystallinitydeterminations used. V Determinations of thechange in the crystallitesize. in the treatedcelluloses show that this decreases from about 210glucose units for the untreatedcotton to about 110 glucose units for thetreated cotton. 4 n

Immersion of the treated cellulose in boiling water for as long as 3hours causes onlya partial restoration of crystallinity provided it hasbeen reduced below that 50%., and with no change in are acceptedasindicative of increased amorphous material, i. e., ofreducedcrystallinity. V

The results of accepted tensile tests made on yarns and cords show that,first, the breaking strength has not been significantly changed by 4 thetreatment; second, the percent elongation.- at-break has been more thandoubled thus resulting in nearly doubling the toughness. These efiectsare in'agreementwith the concept of re-' duced crystallinity.Determination of twist by an accepted method shows that there has beenno significant change in the twist of the yarn by the treatment.

Higher alkyl amines, such as normal hexylamine,.'even though anhydrouswhen used alone 1 as-the treating-agent, do not reduce crystallinity.

However, these higher amines, particularly primary' hexyl and primaryheptylamines, when preceded by a short-chain amine, particularly ianhydrous liquid ethylamine, can efiect a further Varying theproportions will afiect the amount of reduction. Thus, no reductionisiound ifi'th amines. are in the proportions. where the shortchainamine ispresent as 50% or less, .by weight.

Since the short-chain amines-have low boiling points and since acontinuous cyclic methodot extraction is' employed to remove from theswollen cellulosic material such mine. as remains after washing with.the. non-polar solvent. 9. means must be provided t6 prevent. them fromcycling with the. solvent. A suitable. methodoi' doing. this was to formin the. boiling flask Of the extractor a non-volatile amine salt whichmay or may not be soluble in the solvent. Aqueous solutions of acidicmaterial are unsuitable since the presenceofwat r is to beavoided';.vo1au1eami substances are to be avoided for reasons obvioustothose skilled in, the art; whatever the stance, or substances, theremust not bev an adverse reaction withthe solvent. 'Co'ncentratedorthoph'o'sphoric acid plus a small amcunt of phosphoric anhydride wasfound to be suited fer this purpose. Sulfamic acid can serve the purposealso, but concentrated sulfuric acid not suitable since it reactsadversely with the sol.-

vents. w

The fellowi'ng', exam ies, whicha're not t?) be considered as limitihgillustrate the process of treating the 'enumsm fiber.

EmampZe 1,

Approximateiy 10 g. or bleached cotton fiber, obtained from acbm'merciai scurce anc cut to short lengths, was immersed overnight at 5Q. in anhydrous liquid monoethylamine, contained in a screw-cap bottle.No attempt was'made toe-xelude air during the handling or processing.After preliminary removal of the amine bystation, followed by washingand extracting of the remainder with chloroform, the cotton was allowedto dry. The crystallinity of this material was found to be'about 23%. Itwas stillfibrous and visually apparently undamaged; however", byviscosity measurements it was found to show some chemical degradationwhich was attributed to alkaline oxidation due to-expo'sure tc'atmoepheric oxygen. V

I Example 1 1 I About 100 g. of the" out cotton described in Example Iwas immersed for 4' hoursiin anhydrous, liquid'monoethylamine at 0? Q.contained in a vessel open to the atmosphere. Excess amine 5 was removedby suction. The cotton, still damp with ethylamine, was placed in alarge screwcap bottle and then covered with anhydrous normal hexylamine.The bottle and contents were allowed to stand overnight at roomtemperature. The excess hexylamine was removed by suction, then bywashing and extracting with chloroform. No attempts were made to excludeair during the handling and processing. After drying, this material wasfound to have a crystallinity of about 19%, and was still fibrous andapparently undamaged.

Eaample III Approximately g. of cut cotton as described in Example I wasimmersed overnight at room temperature in a mixture of amines. Themixture consisted of 75% by weight of anhydrous monoethylamine and byweight of anhydrous normal hexylamine. The cotton and amine mixture wascontained in a closed glass jar of sufficient strength to withstandconsiderable internal pressure. By morning some pressure had developed,evidently from the high content of ethylamine in the mixture, but thiswas easily vented before attempting to open the jar. The liquid wasremoved by suction, followed by washing and extracting with chloroform.After drying, the fibrous material was found to have a crystallinity of50%.

Example IV Approximately 10 g. of cut cotton, as in Example I, wastreated exactly as given in Example I, with the exception that normalhexane was used instead of chloroform for washing and ex- 1 tracting thetreated material. After air-drying, the crystallinity of the fibrousmaterial was found to'be about 20%.

Example V One pound of raw cotton fiber, in the form of card sliver, wastreated with anhydrous ethylamine. Batches of 100 g. each of the sliver,in continuous form, were immersed 4 hours in the anhydrous amine. Alloperations were carried out under nitrogen, including the first twowashings with chloroform to begin removal of the amine. The remainder ofthe amine was removed by extraction with chloroform. After airdrying,the fiber was found to have a crystallinity of 24%. Critical examinationof the fiber revealed that there was very little degradation. The sliverhad a harsh hand, due to the removal of the waxes by the treatment.

Example VII The exact treatment as described in Example VI above wasrepeated on 10 g. skeins of a 20s singles, kier-boiled cotton yarn ofloose twist.

After drying, the yarn, of undamaged appearance and slightly harsh hand,had a crystallinity of 31%.

Example VIII The exact treatment described in Example VI above wasrepeated on 10 g. skeins of the 20s singles yarn. In this case thecrystallinity of the extracted, dry yarn was 34%. There was littledegradation and only a slightly harsh hand. The yarn was still suitabletextile material as evidenced by tensile tests for breaking strength andelongation.

Having described our invention, we claim:

1. A process of reducing the degree of crystallinity of a native fibrouscellulosic material with no substantial chemical degradation andimpairment of the fibrous structure comprising immersing the cellulosicmaterial in a liquid treating agent selected from the group consistingof an anhydrous primaryalkylamine containing from 1 to 2 carbon atoms,and a mixture of at least by weight of an anhydrous primary alkylaminecontaining from 1 to 2 carbon atoms and an anhydrous primary alkylaminecontaining from 6 to '7 carbon atoms, mechanically separating asubstantial amount of the treating agent from the treated material, andseparating substantially all of the remaining treating agent byextraction with a non-polar organic solvent.

2. The process of claim 1 in which the treating agent is anhydrousprimary metIhylamine.

3. The process of claim 1 in which the treating agent is anhydrousprimary ethylamine.

4. The process of claim 1 in which the treating agent is a mixture of atleast 50% by weight of an anhydrous primary alkylamine containing from 1to 2 carbon atoms and an anhydrous primary alkylamine containing from 6to '7 carbon atoms.

5. The process of claim 1 in which the treating agent is a mixture of atleast 50% by weight of anhydrous primary ethylamine and anhydrousprimary hexylamine.

6. The process of claim 1 in which the nonpolar solvent is chloroform.

7. The process of claim 2 in which the nonpolar solvent is chloroform.

8. The process of claim 3 in which the nonpolar solvent is chloroform.

9. The process of claim polar solvent is chloroform.

10. The process of claim 5 in which the nonpolar solvent is chloroform.

KYLE WARD, JR. CARL M. CONRAD. LEON SEGAL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS 4 in which the non- Number Name Date 2,186,101Dreyfus Jan. 9, 1940 2,200,452 Kosslinger et al. May 14, 1940 2,218,479Peterson Oct. 15, 1940 2,270,326 Miller Jan. 20, 1942

1. A PROCESS OF REDUCING THE DEGREE OF CRYSTALLINITY OF A NATIVE FIBROUSCELLULOSIC MATERIAL WITH NO SUBSTANTIAL CHEMICAL DEGRADATION ANDIMPAIRMENT OFF THE FIBROUS STRUCTURE COMPRISING IMMERSING THE CELLULOSICMATERIAL IN A LIQUID TREATING AGENT SELECTED FROM THE GROUP CONSISTINGOF AN ANHYDROUS PRIMARY ALKYLAMINE CONTAINING FROM 1 TO 2 CARBON ATOMS,AND A MIXTURE OF AT LEAST 50% BY WEIGHT OF AN ANHYDROUS PRIMARYALKYLAMINE CONTAINING FROM 1 TO 2 CARBON ATOMS AND AN ANHYDROUS PRIMARYALKYLAMINE CONTAINING FROM 6 TO 7 CARBON ATOMS, MECHANICALLY SEPARATINGA SUBSTANTIAL AMOUNT OF THE TREATING AGENT FROM THE TREATMENT MATERIAL,AND SEPARATING SUBSTANTIALLY ALL OF THE REMAINING TREATING AGENT BYEXTRACTION WITH A NON-POLAR ORGANIC SOLVENT.